Originally Posted by IKE

Check your repeatability. You want to make sure your shooter is extremely repeatable.
When shooting, sources of error will include distance, alignment, .... ensure your prototype is shooting in the same spot every shot. Find the variables that influence this.

When comparing a 3 point shot versus a 2 point "dunk", your 3 pt. shot needs to be at least 66% as accurrate as what you believe a 2 pt. dunk to be.